1. Field of Invention
The present invention relates to an apparatus used in the fabrication of integrated circuits. More particularly, the present invention relates to a gas delivering apparatus for conducting chemical vapor deposition (CVD).
2. Description of Related Art
Chemical vapor deposition has become one of the most important processes in depositing thin film on semiconductor wafers. Unlike a physical vapor deposition process, which is limited to the deposition of a metallic thin film, all types of thin films required by semiconductor devices, for example, conductive, semi-conductive, or dielectric layers, can be formed by a CVD process. Moreover, the qualities of the deposited layer such as its crystallinity and stoichiometry are better than most other thin film deposition methods.
In general, system for carrying out chemical vapor deposition includes a reactor, a gas supply system, a gas exhaust system and a process control system. For a high-density plasma chemical vapor deposition (HDPCVD) system, the reactor should contain a number of injectors for delivering a gaseous reactant or a mixture of gaseous reactants to the silicon wafer surface. Normally, as soon as a CVD operation starts, the wafer inside the reactor is heated from below and, at the same time, necessary gaseous reactants are delivered to the wafer surface through a system of the injector nozzles. These gaseous reactants are then deposited on the wafer surface, gradually building up a thin layer derived from the reactive materials.
FIG. 1A is a sketch showing a nozzle of a conventional injector. As shown in FIG. 1, the nozzle 10 of a conventional injector is a straight hollow tube. The nozzle 10 serves to deliver a gaseous reactant to the wafer surface for initiating the chemical vapor deposition. However, for this type of design, the maximum spread of the gaseous reactants 12 is quite limited.
FIG. 1B is a sketch showing the distribution of conventional injectors inside a reactor. In a high-density plasma CVD system, the silicon wafer is placed on a wafer stand 14 surrounded by eight injectors 10. As soon as reaction starts, gaseous reactants 12 are injected into the reactor through the nozzles of these eight injectors 10 so that the gaseous reactants 12 can react to form a thin layer on the wafer surface.
FIG. 1C is a top view showing a conventional injector system delivering gaseous reactants to the wafer surface for chemical vapor deposition. As shown in FIG. 1C, a wafer 16 is shown on top of a wafer stand 14, and the gaseous reactants are delivered to the top surface of the wafer 16 through the injector nozzles 10. Because the opening of injector 10 is a straight tube as shown in FIG. 1A, flow rate of the gaseous reactants from the nozzles is quite fast and the spreading range is small. With uneven distribution of gaseous reactants, the rate of distribution in different parts of the wafer surface will be different. Hence, a non-uniform layer will be deposited onto the wafer surface. For example, the deposited thin film in areas 18 and 18' on the wafer 16 is thicker than in other areas.
Since non-uniformity of deposited film can greatly affect the stability of semiconductor devices fabricated on the wafer, this is a highly unsatisfactory gas delivering system.
In light of the foregoing, there is a need to improve the delivery of gaseous reactants.